Centrifugal friction clutch

ABSTRACT

A centrifugal friction clutch having a cup-shaped driven member with a hub receiving a driven shaft and a generally cylindrical driving member freely entered therein for rotation in one direction and comprising two generally semicylindrical shoes, a central hub receiving a driving shaft and a pair of flexible arms extending oppositely outward from the hub between the adjacent flat surfaces of the shoes and connecting the opposite trailing ends of the shoes to the hub, whereby centrifugal force moves the shoes radially into frictional engagement with the annular wall of the cup and whereby the frictional force is increased as the arms flex when stressed between peripheral frictional force and driving torque, both driving and driven members being formed as castings of synthetic plastic material and the cup-shaped driven member having a flexible bottom wall and a long flexible hub which flex to compensate for slight non-parallelism and misalignment of the driving and driven shafts to which the device is connected.

United States Patent 11 1 Roddy et al.

1 51 Jan. 23, 1973 [541 CENTRIFUGAL FRICTION CLUTCH [75] Inventors:Joseph T. Roddy, Ballwin; Wayne L.

Page, St. Louis, both of Mo.

Assignee: Emerson Electric Co., St. Louis, Mo.

Filed: March 15, 1971 Appl. No.: 124,115

[63] Continuation-impart of Ser. No. 858,753, Sept. 17,

1969, abandoned.

U.S. c1 ..192/105 c1), 192/76, 192/107 M I nt. c1. 13jl8 lfl6d 13/18Field ofSearchI. 192/75, 76, 103 a, 104 B, 105 CD, 192/107 M [5 6]References Cited UNITED STATES PATENTS Frantz et a1. ..l92/105 CD Breer..192/105 CD FOREIGN PATENTS OR APPLICATIONS 1,035,480 7/1958 Germany..192/l05 CD PrinYdry Exd miher Allan D. Herrmann Attorney-Charles E.Markham [57] ABSTRACT A centrifugal friction clutch having a cup-shapeddriven member with a hub receiving a driven shaft and a generallycylindrical driving member freely entered therein for rotation in onedirection and comprising two generally semicylindrical. shoes, a centralhub receiving a driving shaft and a pair of flexible arms extendingoppositely outward from the hub between the adjacent flat surfaces ofthe shoes and connecting the oppositetrafling ends of the shoes to thehub, whereby centrifugal force moves the shoes radially into frictionalengagement with the annular wall of the cup and whereby the frictionalforce is increased as the arms flex when stressed between peripheralfrictional force and driving torque, both driving and driven membersbeing formed as castings of synthetic plastic material and thecup-shaped driven member having a flexible bottom wall and a longflexible hub which flex to compensate for slight non-parallelism andmisalignment of the driving and driven shafts to which the device isconnected.

12 Claims, 5 Drawing Figures 1 CENTRIFUGAL FRICTION CLUTCH Thisapplication is a continuation-in-part of my copending application, Ser.No. 858,753, filed Sept. 17, 1969, and now abandoned.

This invention relates generally to centrifugal friction clutches whichform a driving connection between a driving member and a driven memberwhen the driving member attains a predetermined speed. Moreparticularly, the invention relates to a centrifugal friction clutch inwhich shoe elements moved radially into frictional engagement against aresilient bias by centrifugal force to effect a driving connection areconnected to a driving hub portion by resilient arms formed integralwith the shoes and hub portion as a casting of suitable material.

Tl-IE PRIOR ART German Patent No. 1,035,480 to Zimmerman discloses acentrifugal frictional governor having an immovably fixed cup memberconstructed of synthetic plastic material and a rotating membercomprising a pair of weighted shoe portions, a hub portion, and longflexible arms connecting the shoe portions with the hub portion, allformed integral as a casting of synthetic plastic material. The hubportion of the rotating member is connected to a rotating drivingmechanism, the speed of which is to be governed or limited by thedevice. In operation the frictional force between the shoes and thestationary cup member varies as the speed of the rotating member, due tocentrifugal force, until a balance is reached between the torsionalforce of the driving means and the frictional force, whereafter thespeed remains constant in the absence of other variables.

To operate satisfactorily, the frictional force must be purely afunction of the centrifugal force developed; that is to say, thetransmission of any radial force components of the driving torque to theshoes through the connecting arms would, due to the flexibility of theconnecting arms, unpredictably increase the frictional force andtherefore render the governed speed unpredictable. In order to precludethe transmission of any such radial force components of the drivingtorque to the shoes, Zimmerman has connected the leading end of hisshoes with the hub portion, as indicated-by the direction arrow 19 inFIG. 2 of his drawing and as stated in column 4, lines 14 and 15, of hisdescription. This arrangement, in which the shoes are pulled along thefrictional surface instead of being pushed, permits the employment ofthe long, flexible arms shown in Zimmermann, which provide the smoothaction desirable in a device of this kind.

Rotation of the Zimmermann device in a direction opposite to thatindicated would result in flexing and wrapping up of the long, flexible,connecting arms when frictional resistance at the shoe elements due tocentrifugal force is encountered. This apparently would result in arapid increase in the area of frictionally engaging surfaces and astalling of the rotating member. The rotating member of Zimmermannemployed as the driving member of a centrifugal friction clutch wouldnot permit reliable predetermination of the speed at which a drivingconnection capable of driving a predetermined load would be effected.

SUMMARY OF THE INVENTION Inasmuch as the centrifugal force developed ina centrifugal friction clutch varies directly with the weight and radiusof rotation of the shoe elements and as the square of their speed, thediameter of the device and the'weight and speed of the shoes may beconsiderably reduced by supplementing the centrifugal force with radialcomponents of the driving torque transmitted to the shoes through theirflexible connecting arms to effect the frictional force required for adriving connection. This supplementary force being effected by theflexing of the connecting arms when stressed between driving torque andreacting frictional force as the shoes are pushed along the surface actsto further increase the flexing of the arms and, therefore, increasesvery rapidly. The design and arrangement of the radially movable shoesand their flexible connecting arms is therefore quite critical if adriving connection is to be effected smoothly at a desired speed. Thisis particularly so in an economical construction of the driving memberin which the shoes, the connecting arms, and the hub portion are formedas an integral casting of synthetic plastic material.

According to a preferred form of the present invention, the clutchcomprises a cup-shaped driven member havingan annular side wall, abottom wall, and a long externally extending hub member receiving adriven shaft at. its end, a driving member rotating in one directionloosely entered into the driven member and comprising a pair ofgenerally semicylindrical shoes, a hub portion receiving a drivingshaft, and a flexible arm connecting the trailing end of each shoe withthe hub portion. The bottom wall and the long hub of the cupshapeddriven member are made flexible so that its annular side wall may tiltand move laterally slightly to compensate for slight misalignment andnon-parallelism of the driving and driven shafts to which the clutch isconnected.

The shoes are segments of a cylinder and are made just sufficiently lessthan semicylindrical to provide a space between the adjacent flat sidesthereof for the positioning and flexing of a pair of generally straightflexible connecting arms extending oppositely from the hub portion toconnections with opposite ends of the shoes. By making the shoesgenerally semicylindrical, the maximum size and, therefore, mass isattained in the available space.

In this arrangement the intermediate portions of the arms flex in onedirection and the outer ends including small radius curves joining theouter ends of the arms to the shoes flex oppositely as the shoes moveradially, due to centrifugal force, to efiect frictional engagement ofthe arcuate shoe surfaces with the annular wall of the An object of theinvention is to provide a centrifugal friction clutch of particularlysimple and low-cost construction comprising only two parts formed ascastings of synthetic plastic materials.

A further object is to provide a centrifugal friction clutch having acup-shaped driven member and a cylindrical driving member entered intothe driven member comprising a pair of semicylindrical shoes connectedat their opposite ends to a central hub by flexible connecting armslying between the flat sides of the adjacent shoes, and in which theshoes, the hub, and the connecting arms are formed integral as a castingof synthetic plastic material. I

A further object is to provide a centrifugal friction clutch ascharacterized in the preceding paragraph in which the trailing ends ofthe shoes are connected to the hub.

A further object is to provide a centrifugal friction clutch comprisinga cup-shaped driven member having an annular side wall, a bottom wall,and a hub member formed as an integral casting of syntheticthermoplastic material, and a generally cylindrical driving memberentered loosely into the driven member comprising a pair of generallysemicylindrical shoes, a central hub portion, and a pair of flexiblearms lying between the shoes and connecting the opposite trailing endsof the shoes to the hub, in which both the driven and driving membersare castings of synthetic plastic material.

A further object is to provide a centrifugal friction clutch ascharacterized in the preceding paragraph in which small particles ofother materials are embedded in the synthetic plastic material of whichboth members are constructed, which particles increase the elasticityand strength of the material and in which the material of the drivenmember includes small metal particles which increase the dissipation ofheat and reduce the wear at frictionally engaging surfaces.

A further object is to provide a centrifugal friction clutch ascharacterized in the penultimate paragraph in which the bottom wall ofthe cup-shaped member is flexible and in which the hub member isrelatively long and flexible, thereby to permit slight tilting andlateral movement of the annular side wall of the cup to compensate forslight misalignment and non-parallelism of the driving and driven shaftsto which the clutch members are connected.

Further objects and advantages will appear from the followingdescription when read in connection with the accompanying drawing.

In the drawing:

FIG. 1 is a longitudinal cross-sectional view of a centrifugal frictionclutch constructed in accordance with the present invention;

FIG. 2 is an end elevational view of the driven member;

FIG. 3 is a-longitudinal cross-sectional view of the driving member; and

FIG. 5 is a longitudinal cross-sectional view of the driving membertaken along line 5--5 of FIG. 4.

Referring to the drawing, a generally cup-shaped driven member,generally indicated at in FIG. 1, is shown alone in FIGS. 2 and 3.Driven member 10 is formed as a casting of synthetic plastic materialand comprises a relatively thick annular side wall portion or drum 12having a true circular interior surface 14, a

concentric, exteriorly extending, relatively long, hollow hub 16, and abottom wall 18 connecting the drum and hub. The long hollow hub 16 isrelatively flexible and is provided with a short non-circular bore 20 atits outer end adapted to receive the non-circular end of a driven shaft22. The bottom wall 18 is considerably thinner than the annular sidewall 12 and is provided with circularly arranged perforations 24 whichrender the wall 18 relatively flexible. The flexibility of the bottomwall 18 permits the annular wall portion 12 to be tilted slightly withrespect to the axis of the hub 16 and the flexibility of the long hub 16permits the slight lateral movement of the annular wall portion 12 withrespect to the axis of a driven shaft inserted in the end of the hub.The driven member 10 is further provided with a central internallyextending guide pin 25.

A driving member generally indicated at 26 is shown alone in FIGS. 4 and5. Driving member 26 is also formed as a casting of synthetic plasticmaterial and includes a pair of generally semicylindricalshoes 28, a hub30, and a pair of flexible connecting members or arms 32 resilientlyconnecting opposite ends of the shoes 28 tothe hub 30. The hub 30 has around bore 31 entering from one end which freely receives the guide pin25 and a non-circular bore 34 entering from its other end adapted toreceive the non-circular end of a driving shaft 36. I

Referring to FIG. 4, each of the shoes 28 has an intermediate, slightlyraised, arcuate surface portion 42 having a slightly greater radius thanthat of the end portions of the arcuate shoe surfaces. The radius of thearcuate surface portion 42 is substantially the same as that of theinside surface of the annular wall 12 of the driven member while theradii of the end portions of the arcuate shoe surfaces are slightlyless. The diametral dimension between the surface portions 42 issomewhat less, however, than the inside diameter of the annular sidewall 12 of the driven member when the driving member is unstressed, sothat the driving member is entered loosely into the driven member.

The shoes 28 are actually segments of a cylinder which are made justsufficiently less than semicylindrical to provide sufficient spacebetween their flat sides for the positioning and flexing of the arms 32.The arms 32 are preferably substantially straight and lie substantiallyparallel with the straight sides of the shoes. Clearance is alsoprovided between the hub 30 and the shoes 28 by the provision of arcuaterecesses 44 in the straight sides of the shoes. The flexible members 32extend oppositely from the hub 30 and are connected to opposite ends ofthe shoes 28 through arcuate portions 33 of small radii.

While other suitable synthetic plastic materials may be used, we preferto form the driven member 10 as a casting of suitable synthetic materialhaving embedded therein glass fibers and to form the'driving member26 asa casting of different suitable synthetic plastic material havingembedded therein glass fibers and metal chips. The strength andelasticity required in the driving member is attained by including theglass fibers. It was found that by constructing the driven'member of adifferent synthetic plastic material than that of the driving membergreater frictional force could be developed between the shoes and thedriven member due to centrifugal force. This is desirable in that itpermits employing less flexible connecting arms, thereby permitting thetransmission of greater driving torque. Constructing the driven memberof a polyurethane thermoplastic material provided this increasedfrictional force, but lacked the required structural strength and tendedto heat unduly along its frictionally engaged surface to the extent thatit softened and bailed up.

However, by adding glass fibers and small metal particles in sufficientquantity to polyurethane in a molten state, a composite material havingthe required structural strength and the ability to disperse andtransfer the heat of friction sufficiently from the engaging surface toovercome the heating problem resulted. Also, it was found that theaddition of small metal particles substantially reduced the rate of wearat the frictionally engaged surface.

OPERATION The clutch may be used, for example, as a driving connectionbetween a low-cost electric motor having a low starting torque and aliquid displacement pump, in which the shaft 22 in FIG. 1 is the pumpimpeller shaft and the shaft 36 is the motor shaft. The device is shownin a still condition in FIG. 1, in which condition there is a diametralclearance between the surfaces 42 of shoes 28 and the annular wall 14 ofthe driven member and a somewhat smaller diametral clearance between thecentral guide pin 25 and the bore 31 in hub 30. The driving member is,therefore, free to rotate in the driven member at low speeds, but isprevented from rattling against the wall of the driven member.

When the electric motor is started, the driving member 26 is-rotatedfreely in the direction indicated by the arrows in FIG. 4. At low speedthe driving member may float axially slightly in the driven member dueto end play in the motor shaft. To prevent engagement of the inner faceof the shoes 28 with the bottom wall of the cup, a small diametercircular portion 46 raised slightly from the bottom wall of the drivenmember is provided, whereby the inner end of hub 30 engages the portion46 when the driving member moves axially inward.

As the speed of the electric motor increases to a predetermined speedsomewhat less than its maximum no-load speed, the shoes 28 are movedradially outward by centrifugal force and into engagement with thesurface 12 of the driven member with sufficient radial force to effectan initial frictional force opposing rotation of the driving member. Asthe shoes 28 move radially outward from their still positions intoengagement with the wall 12, the intermediate portions of the connectingarms flex with their outer ends moving in the direction of rotation.This tends to tilt the leading end of the shoes slightly inward.However, the outer ends of the arms including the small radius curvedportions or bights 33 connecting the outer ends of the arms to the shoesalso flex but in an opposite direction, thereby compensating the tiltingof the shoes so that the centers of curvature of the arcuate shoeportions 42 move radially substantially along a straight lineintersecting the center of curvature of wall 12.

When the initial frictional force is established by centrifugal force ata predetermined motor speed, the resistance of the load acting throughthis frictional force stresses the connecting arms 32 so that theirouter ends try to flex in a direction opposite to the direction ofrotation. This flexing effects the application of radial components ofthe driving force to the shoes, thereby increasing the frictional force.This increased frictional force in turn further stresses and flexes thearms. The action is cummulative until the load is overcome.

The semicylindrical form of the shoes 28 utilizes the available space toprovide the required mass to effect the initial frictional force withoutthe necessity of adding weighting material having greater specificgravity than the synthetic plastic material of the shoes. The provisionof the intermediate arcuate contacting portions 42 on the shoes providessmoother engagement of the driving member and precludes the frictionalengagement or digging in of the leading ends of the shoes which mayotherwise effect a jolting engagement of the driving member withobjectionable impact force. In event the driving and driven shafts towhich the device is connected are not exactly parallel or exactlyaligned, which frequently occurs, the bottom wall and long hub 16 of thedriven member will flex to compensate for this.

We claim:

1. A centrifugal friction clutch comprising a driven member having anannular wall and a driving member of general cylindrical form looselyentered into said annular wall, said driving member being adapted torotate in one direction and being formed as a casting of syntheticplastic material and comprising as integral portions thereof a pair ofshoe members of general semicylindrical form with flat sides facing eachother in spaced relationship, a central hub member adapted to receive adriving shaft, and a flexible arm connecting each of said shoes to saidhub, said connecting arms extending oppositely and radially from saidhub between the adjacent flat sides of said shoes to connection with theopposite trailing ends of said shoes whereby said shoes are movableradially to engage said annular wall, said shoes being segmentssufiiciently less than semicylindrical to provide spacebetween the flatsides thereof for the positioning and flexing of said arms and the flatsides of said shoes being recessed to provide clearance for said hub.

2. The clutch claimed in claim 1 in which said connecting arms aresubstantially straight and spaced from coextending portions of the flatshoe surfaces and each including a short arcuate portion at its'outerend connecting its outer end with the end of its respective shoe.

3. The clutch claimed in claim 1 in which said driven member is acup-shaped member formed as a casting of synthetic plastic material andincludes in addition to said annular wall as integral portions thereof acentral hub for receiving a driven shaft and a bottom wall joining saidhub with said annular wall.

4. The clutch claimed in claim 1 in which the plastic material of whichsaid driving member is formed includes glass fibers dispersed therein insufficient quantity to provide the elasticity required in saidconnecting arms to permit outward travel of said shoes under centrifugalforce with sufficient recovery force to retract them and to provide thestrength required in said connecting arms to transmit the torque withoutundue flexing.

5. The clutch claimed in claim 3 in which said driven member is formedof a synthetic plastic material other than the material of which saiddriving member is formed, and which includes dispersed therein smallmetal particles in an amount to substantially increase dissipation ofheat developed in small local areas of the frictionally engaged surface.

6. The clutch claimed in claim in which the material of which saiddriven member is formed further includes dispersed therein glass fibersin an amount necessary to attain the flexibility and strength required.

7. In a centrifugal friction clutch, a cup-shaped driven membercomprising an annular side wall, a bottom wall, and a hub receiving adriven shaft, a generally cylindrical driving member loosely enteredinto said driven member and comprising a pair of generallysemicylindrical shoes with flat sides facing each other in spacedrelationship, a central hub, and a pair of flexible arms connecting theopposite ends of the shoes with the hub whereby the shoes are movedradially outward by centrifugal force into engagement with said annularwall, driving means including a drive shaft entered into said centralhub operative to drive said driving member in a predetermined directionof rotation, said flexible arms being substantially straight andextending radially between the adjacent flat sides of said shoes andconnecting that end of each shoe with said hub member which is trailingwith respect to said predetermined direction of rotation.

8. The subject matter claimed in claim 7 in which said driven member isformed as a casting of synthetic plastic material and in which saidbottom wall is flexible, thereby to permit tilting of the annular sidewall to compensate for slight non-parallelism of said driving and drivenshafts.

9. The subject matter claimed in claim 7 in which said hub of saiddriven member is relatively long and flexible whereby it flexes tocompensate for any slight misalignment of said driving and drivenshafts.

10.The subject matter claimed in claim 7 in which said driven memberfurther includes an internal axially extending guide pin and in whichsaid hub of said driving member includes an axial bore receiving saidguide pin, the fit of said guide pin in said hub being such as to permitthe free rotation of the driving member therein while preventing contactof the driving member with the annularwall of the driven member whensaid driving member is in a retractedposition.

11. The subject matter claimed in claim 7 in which the arcuate surfacesof said generally semicylindrical shoes each include an intermediate,raised, arcuate surface portion arranged to frictionally engage saidannular wall of said driven member and to space the remainder of thearcuate shoe surface from said annular wall.

12. The subject matter claimed in claim 11 in which said raised arcuatesurface portionshave a radius substantially equal to the radius ofcurvature of said annular wall of said driving member.

i t I t k

1. A centrifugal friction clutch comprising a driven member having anannular wall and a driving member of general cylindrical form looselyentered into said annular wall, said driving member being adapted torotate in one direction and being formed as a casting of syntheticplastic material and comprising as integral portions thereof a pair ofshoe members of general semicylindrical form with flat sides facing eachother in spaced relationship, a central hub member adapted to receive adriving shaft, and a flexible arm connecting each of said shoes to saidhub, said connecting arms extending oppositely and radially from saidhub between the adjacent flat sides of said shoes to connection with theoPposite trailing ends of said shoes whereby said shoes are movableradially to engage said annular wall, said shoes being segmentssufficiently less than semicylindrical to provide space between the flatsides thereof for the positioning and flexing of said arms and the flatsides of said shoes being recessed to provide clearance for said hub. 2.The clutch claimed in claim 1 in which said connecting arms aresubstantially straight and spaced from coextending portions of the flatshoe surfaces and each including a short arcuate portion at its outerend connecting its outer end with the end of its respective shoe.
 3. Theclutch claimed in claim 1 in which said driven member is a cup-shapedmember formed as a casting of synthetic plastic material and includes inaddition to said annular wall as integral portions thereof a central hubfor receiving a driven shaft and a bottom wall joining said hub withsaid annular wall.
 4. The clutch claimed in claim 1 in which the plasticmaterial of which said driving member is formed includes glass fibersdispersed therein in sufficient quantity to provide the elasticityrequired in said connecting arms to permit outward travel of said shoesunder centrifugal force with sufficient recovery force to retract themand to provide the strength required in said connecting arms to transmitthe torque without undue flexing.
 5. The clutch claimed in claim 3 inwhich said driven member is formed of a synthetic plastic material otherthan the material of which said driving member is formed, and whichincludes dispersed therein small metal particles in an amount tosubstantially increase dissipation of heat developed in small localareas of the frictionally engaged surface.
 6. The clutch claimed inclaim 5 in which the material of which said driven member is formedfurther includes dispersed therein glass fibers in an amount necessaryto attain the flexibility and strength required.
 7. In a centrifugalfriction clutch, a cup-shaped driven member comprising an annular sidewall, a bottom wall, and a hub receiving a driven shaft, a generallycylindrical driving member loosely entered into said driven member andcomprising a pair of generally semicylindrical shoes with flat sidesfacing each other in spaced relationship, a central hub, and a pair offlexible arms connecting the opposite ends of the shoes with the hubwhereby the shoes are moved radially outward by centrifugal force intoengagement with said annular wall, driving means including a drive shaftentered into said central hub operative to drive said driving member ina predetermined direction of rotation, said flexible arms beingsubstantially straight and extending radially between the adjacent flatsides of said shoes and connecting that end of each shoe with said hubmember which is trailing with respect to said predetermined direction ofrotation.
 8. The subject matter claimed in claim 7 in which said drivenmember is formed as a casting of synthetic plastic material and in whichsaid bottom wall is flexible, thereby to permit tilting of the annularside wall to compensate for slight non-parallelism of said driving anddriven shafts.
 9. The subject matter claimed in claim 7 in which saidhub of said driven member is relatively long and flexible whereby itflexes to compensate for any slight misalignment of said driving anddriven shafts.
 10. The subject matter claimed in claim 7 in which saiddriven member further includes an internal axially extending guide pinand in which said hub of said driving member includes an axial borereceiving said guide pin, the fit of said guide pin in said hub beingsuch as to permit the free rotation of the driving member therein whilepreventing contact of the driving member with the annular wall of thedriven member when said driving member is in a retracted position. 11.The subject matter claimed in claim 7 in which the arcuate surfaces ofsaid generally semicylindrical shoes each include an intermediate,raised, arcuate suRface portion arranged to frictionally engage saidannular wall of said driven member and to space the remainder of thearcuate shoe surface from said annular wall.
 12. The subject matterclaimed in claim 11 in which said raised arcuate surface portions have aradius substantially equal to the radius of curvature of said annularwall of said driving member.